1. Field of the Invention
This invention relates to apparatus for preventing freezing of water to provide access to drinking water for stock and to control the filling of stock tanks, and more particularly to such apparatus utilizing heat pipes having large heat transfer surface areas.
2. Description of the Prior Art
One of the severe problems encountered by cattlement is providing a source of water to their cattle, especially in the winter months. Commonly, water is provided in stock tanks, which are readily available and widely used. However, in the winter months, ice forms on the surface of the water in the stock tanks, and the cattle often are unable to break through the ice. Thus, the cattlemen must travel, sometimes several times a day in severely cold weather, to the tanks to break through the ice to the unfrozen water. This is a difficult and time consuming job, especially when the watering tanks are at remote locations, and when the ice thickness is of several inches.
In the summer months, although not as great a problem, the sun may heat the water to a temperature which the cattle find too warm, and they refuse to drink the water, which results in weight loss and other problems. Additionally, because of the warm summer sun, algae and other vegetative growths occur in the tank, which require special cleaning and other time consuming procedures.
The annoyance of the wintertime freezing problem has spawned several proposed solutions. For example, Baer in U.S. Pat. No. 3,618,569, proposes a continuous loop completely filled with fluid. Baer recognizes that water changes density at temperatures close to its freezing point. Before the water freezes, it becomes more dense, and sinks to a lower fluid level. As the water lowers in temperature, it becomes less dense, seeking a higher fluid level until it freezes, at which time the ice forms, beginning at the surface of the water. Thus, a temperature gradient exists in water near its freezing point, being increasinly warmer away from the surface. The Baer device is intended to carry the heat from the lower warmer fluid location to the surface, to retard the surface freezing. It is a continuous loop filled with fluid, such as alcohol, which circulates within the loop by convection. The loop, however, is symmetrical and is a balanced gravity system which carries, in practice, very little heat to the surface. It is therefore operable only for very minor freezing conditions.
Heat pipes have been proposed to retard ice formation, in such applications as on paving, or the like, in Tippmann, U.S. Pat. No. 3,195,619. Tippmann employs a number of elongated heat pipes extending into the ground beneath the pavement, and having a portion located within the paving material itself. The heat pipe has a fluid contained partially therewithin, which is evaporated by the warmer earth temperatures beneath the pavement. The vapor, seeking a lower partial vapor pressure within the pipe, rises to the region of the pipe within the pavement, whereupon, it gives up its heat to the pavement and condenses, flowing back downwardly to the lower warmer region of the pipe. The condensing of the fluid presents sufficient heat to keep the ice on the pavement melted, according to Tippmann.
The Tippmann heat pipe suggestion, however, is not practical in stock tank configurations for several reasons. First, the heat pipes disclosed by Tuppmann are of relatively small diameter. Consequently, unless a large number of such pipes were employed, an insufficient amount of heat would be transferred to the water within the tank. Even so, it is questionable whether a sufficient quantity of heat in the vicinity of a small diameter pipe in the ground exists to actually prevent ice formation in relatively extreme or severe temperature environments. Furthermore, even if such heat pipe were to be employed, the size of the opening in the ice would be too small to be useful for the cattle to gain access to the unfrozen water.
Another problem which is encountered during the winter is in the filling of the water tank, or in the maintaining of the fluid level within the tank. Ordinarily, stock tanks have a fill valve centrally located adjacent the bottom of the tank which is controlled by a float which, due to its buoyancy, is at the surface of the water within the tank. As the water level is depleted, the float decreases its distance from the fill valve, turning the valve on to fill the tank until a sufficient quantity of water is injected into the tank to raise the float to turn the valve off. However, during the winter months, the float becomes completely frozen into an ice layer across the top of the tank. Consequently, if the water level decreases to the point where the valve turned on, the valve may continue to run, since the float often becomes frozen in position, resulting in continual overflowing of the stock tank.